Multi-Stream Microchannel Device

ABSTRACT

Provided is a process and device for exchanging heat energy between three or more streams in a microchannel heat exchanger which can be integrated with a microchannel reactor to form an integrated microchannel processing unit. The combining of a plurality of integrated microchannel devices to provide the benefits of large-scale operation is enabled. In particular, the microchannel heat exchanger enables flexible heat transfer between multiple streams and total heat transfer rates of about 1 Watt or more per core unit volume expressed as W/cc.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of, and claims priority to, U.S. application Ser. No. 10/222,604, filed Aug. 15, 2002, now U.S. Pat. No. 7,014,835, and claims priority to U.S. patent application Ser. No. 11/300,914, filed Dec. 15, 2005, now U.S. patent Ser. No.______, which is a divisional of, and claims priority to, U.S. application Ser. No. 10/222,604, filed Aug. 15, 2002, entitled “Multi-Stream Microchannel Device”, now U.S. Pat. No. 7,014,835, which is related to the following commonly-assigned applications filed concurrently therewith on Aug. 15, 2002: “Integrated Combustion Reactors and Methods of Conducting Simultaneous Endothermic and Exothermic Reactions”, Attorney Docket No. 02-052, now U.S. Pat. No. 7,250,151, and “Process for Cooling a Product in a Heat Exchanger Employing Microchannels for the Flow of Refrigerant and Product”, Attorney Docket No. 01-002, now U.S. Pat. No. 6,622,519, which applications are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to microchannel devices and processes for multi-stream heat exchange and particularly to multi-stream heat exchange in combination with chemical reaction and more particularly to multi-stream heat exchange in combination with endothermic chemical reactions such as reforming and more particularly to endothermic reactions coupled with exothermic reactions such as combustion.

BACKGROUND OF THE INVENTION

Heat exchangers are critical components in virtually all unit operations involving fluid (gas or liquid) streams. They become even more critical when it is desired to add heat or thermal energy or take away heat or thermal energy from a chemical reaction. For example, endothermic reactions often require, or benefit from, the addition of heat energy. Exothermic reactions, on the other hand, often require, or benefit from, the removal of heat energy. Owing to the economic importance of many such chemical reactions, there is a continual quest for improved performance, both in terms of conversion of reactants to products and in terms of selectivity to desired products relative to undesired products.

MicroChannel Technology (MCT) has been demonstrated to provide many such benefits and recent years have seen a significant increase in the application of MCT to many unit operations. See, e.g., A. A. Rostami et al., Flow and Heat Transfer for Gas Flowing In Microchannels: A Review, 38 Heat and Mass Transfer 359-67 (2002) (applications in medicine biotechnology, avionics, consumer electronics, telecommunications, metrology, and many others) and R. S. Wegeng et al., Compact Fuel Processors for Fuel Cell Powered Automobiles Based on Microchannel Technology, Fuel Cells Bulletin No. 28 (2002) (compact hydrogen generators for fuel cells). MCT utilizes microchannel devices for carrying out processes that had previously been constrained to far larger equipment; often three to 1,000 times as large for comparable total throughput. MCT devices, which contain features of at least one internal dimension of width or height of less than about 2 mm and preferably less than about 1 mm, have the potential to change unit operations in ways analogous to the changes that miniaturization has brought to computing technology. MCT can be used to advantage in small-scale operations, such as in vehicles or personal (portable) devices. Importantly, too, MCT systems that can be economically mass-produced and connected together to accomplish large-scale operations are very desirable.

More particularly, heat exchangers have become smaller and smaller with more heat energy transferred per unit volume due to the additional area of smaller channels in heat exchangers. Earlier technology includes so-called compact heat exchangers. See, e.g., V. V. Wadekar, a ChE's Guide to CHEs, Chemical Engineering Progress, December 2000, 30-49. Compact heat exchangers provide heat energy transfer rate densities, or heat energy transfer rate per unit volume (thermal power density) (where the volume is the total core volume as defined herein below), only up to about 0.4 W/cc for gas-phase exchangers. MCT heat exchangers, by comparison, provide heat energy transfer rate densities (thermal power density) of about 1 W/cc to 40 W/cc. Compact heat exchangers also have low interstream planar heat transfer percents, typically less than 10 percent. MCT heat exchangers, by comparison, have much higher interstream planar heat transfer percents, typically greater than 10 percent, preferably greater than 20 percent, more preferably greater than 40 percent, and even more preferably greater than 50 percent. In addition, MCT heat exchangers can rely on smaller average approach temperatures when producing the higher thermal power densities.

The above disadvantages of compact heat exchangers can be overcome by the use of MCT heat exchangers. There are problems, however, even with existing MCT heat exchangers. For example, MCT heat exchangers have not been designed which can process more than two separate streams in a single integral device. Processing three or more streams in a heat exchanger can, for example, enable unequal heat gain and loss between the three or more streams. Thus, when it is desirable to transfer heat energy between three or more streams, a compact heat exchanger must be employed or multiple two-stream MCT heat exchangers must be employed. Even multiple two-stream MCT heat exchangers, however, allow significantly more heat transfer to the ambient and the necessary stream transfer piping can cause higher pressure drops to redistribute flows or dead zones and eddies which can cause extended residence times. These extended residence times can cause fouling, corrosion, erosion, decomposition, formation of undesirable byproducts, and, for example, coke can be deposited when processing carbon-containing streams at elevated temperatures. Furthermore, for MCT heat exchangers to realize their full potential, they must be combined in significant numbers to be scaled up to economic large-scale operations. Thus, owing to having a large number of small MCT heat exchangers in close proximity and the close proximity of one channel to another, manifolding the streams entering and exiting an MCT heat exchanger (or any MCT device) becomes a problem.

The manifold design objective is to provide for acceptably uniform flow through a device with an acceptable manifold geometry and stream mechanical energy losses. See, W. M. Kays and A. L. London, Compact Heat Exchangers, 3d ed., at 41 (1984). Restated, manifold design requires tradeoffs among device performance factors as affected by flow uniformity, overall pressure drop, and manifold size and complexity. For example, device performance could be heat transfer performance in the case of endothermic reactions coupled with exothermic reactions within an MCT device. As will be appreciated by those skilled in the art, the manifold design for any given stream is readily approached through application of fluid dynamics. Kays at 41-43.

When manifolding multiple streams in MCT devices, the design problem becomes even greater than designing a two-stream manifold. Having more streams present in a device means proportionally less of the external surface area of that device is available for accessing each stream. The compactness of an MCT device works against the geometric spacing requirements needed to seal manifolds to prevent stream-to-stream leakage. The manifold design must, therefore, address both the design objective stated herein above, as well as the limited external surface area.

Heat exchangers are not the only unit operation to benefit from the push toward miniaturization. Closely related, reactors, too, have begun to shrink in size substantially and with excellent results. Wegeng at 9-12 (vaporizers, reforming reactors, and steam reforming). There remain, however, special problems involving MCT reactors and the need for heat transfer. For example, thermal stresses pose significant problems. MCT devices are manufactured and assembled to much higher tolerances than comparable conventional large-scale devices and multiple MCT devices must be closely-packed to economically match the throughput of comparable to large-scale devices. (An MCT device, while producing high output per core unit volume of the device, typically must be combined in very high numbers to provide comparable throughput.) Thus, temperature differentials that could be easily tolerated by a conventional device of greater dimensions can produce unacceptable thermal stresses in an MCT device which is smaller and thus experiences a much higher temperature gradient. Illustratively, an MCT reactor that is overly constrained geometrically either by multiple integral heat exchangers or integrally-combined multiple integral MCT heat exchanger/reactor units can be subjected to potentially destructive thermal stresses. In general, as a result of the increased efficiency of MCT heat exchangers, they exhibit high temperature gradients with corresponding high thermal stresses. To solve this problem, heat exchangers have been “de-coupled” from the reactors to allow for thermal expansion. In doing so, however, separate piping or tubing is required. As a result, as with multiple two-stream MCT heat exchangers, there can be significant heat loss between multiple units to the ambient and through associated piping or tubing. As noted herein above, such piping connections can become sites for fouling and coke-formation problems. Alternatively, more expensive metals that can tolerate the thermal stresses or inexpensive throwaway devices must be employed.

In addition, the goal of combining multiple heat exchanger/reactor devices to provide economically high total throughput has proved to be elusive. See, e.g., O. Woerz, Microreactors as Tools in Chemical Research, in Microreaction Technology, IMRET 5: Proceedings of the Fifth International Conference on Microreaction Technology at 385 (Michael Matlosz et al. eds. October 2001) (“In principle, [it is conceivable that microreactors can also be used for production]. However, serious problems would be encountered.”). In the petroleum processing industry, for example, even minimally-sized specialty units, for, for example, hydrogen production, typically have a capacity of at least one million standard cubic feet per day (scfd) of hydrogen up to about 100 million scfd of hydrogen. A single-stream MCT device, in contrast, produces, at most, 1,000 to 10,000 scfd of hydrogen. Therefore, to provide comparable throughput, a system must comprise from 100 to up to 100,000 closely-integrated arrays of microchannel units.

The present invention overcomes the drawbacks of the prior art of having to provide multiple two-stream heat exchangers with the necessary inter-unit piping, the inability of integrating an MCT heat exchanger with an MCT reactor, and combining a plurality of integrated MCT heat exchanger/reactor devices to form an MCT system to gain the benefits of large-scale operation, that is, high throughput to equal large-scale operations. In doing so, significant thermal power density with multiple streams is achieved, heat loss to the ambient is reduced, corrosion, erosion, decomposition, and coke formation are reduced or eliminated, and higher throughput per unit volume is attained. In addition, thermal stresses are reduced by operating devices with a monotonically increasing temperature profile.

BRIEF DESCRIPTION OF THE INVENTION

Included is a process and device for exchanging heat energy between three or more streams in an MCT heat exchanger, integrating the MCT heat exchanger with an MCT reactor to form an integrated MCT processing unit, combining a plurality of integrated MCT processing units into an integrated MCT processing system, and finally combining a plurality of integrated MCT systems into an MCT processing stack to provide the benefits of large-scale operation. Particularly, the MCT heat exchange process and device enables flexible heat transfer between multiple streams and total heat transfer rates of about 1 Watt (W) or more per core unit volume (cubic centimeters (cc)) (W/cc), pressure drop on the order of about 0.25 psi per in. or less, stream Reynolds Numbers in the transition or laminar zones, and interstream planar heat transfer percents of greater than about 30 percent. In some embodiments, the integrated MCT heat exchanger and MCT reactor exhibits a monotonically increasing temperature profile and, thus, thermal stresses are minimized.

In one embodiment, an apparatus comprises a first microchannel, having an inlet thereto and an outlet therefrom; a second microchannel, having an inlet thereto and an outlet therefrom; and at least a third microchannel, having an inlet thereto and an outlet therefrom, wherein each inlet and each outlet is distinct from the other inlets or outlets, respectively.

In a further embodiment, a process comprises flowing a first stream, having a first temperature, through a first microchannel; flowing a second stream, having a second temperature, through a second microchannel; flowing at least a third stream, having an at least third temperature, through an at least third microchannel; and placing the first stream in thermal communication with the second stream and the at least third stream.

In a further embodiment, a process, comprises flowing a first fluid through a plurality of first microchannels; flowing a second fluid through a plurality of second microchannels; and flowing at least a third fluid through a plurality of at least third microchannels, the plurality of at least third microchannels being in thermal communication with the plurality of first microchannels and with the plurality of second microchannels.

In a further embodiment, an apparatus comprises a first end and a second end; a first microchannel; a second microchannel; a third microchannel; a fourth microchannel; a fifth microchannel; a sixth microchannel; and a seventh microchannel, each microchannel defining a passageway between the first end and the second end, wherein each microchannel is in thermal communication with at least one of the other microchannels and the first microchannel has a cross-sectional area different from at least the second microchannel.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a perspective view of a heat exchanger according to the present invention.

FIG. 1 b is a perspective section view at section 1 b-1 b of the perspective heat exchanger shown in FIG. 1 a.

FIG. 1 c is a plan view of the heat exchanger shown in FIG. 1 a.

FIG. 1 d is a schematic perspective view of the heat exchanger shown in FIG. 1 a illustrating counter-/co-flow operation.

FIG. 2 a is a perspective view of a cross-flow heat exchanger according to a further embodiment of the present invention.

FIG. 2 b is a perspective section view of the cross-flow heat exchanger shown in FIG. 2 a at section 2 b-2 b.

FIG. 2 c is a schematic perspective view of the cross-flow heat exchanger shown in FIG. 2 a illustrating co-/cross-flow operation.

FIG. 3 a is a cross-section view of an MCT device having a heat exchange portion and a reaction portion in combination according to the present invention.

FIG. 3 b is a cross-section view of an MCT device having a heat exchange portion and a reaction portion in combination having a reverse orientation of the MCT device illustrated in FIG. 3 a.

FIG. 4 is a cross-section view of an MCT device having a heat exchange portion and a reaction portion in combination according to a further embodiment of the present invention.

FIG. 5 is a cross-section view of an MCT processing system having a heat exchange portion and a reaction portion in combination according to the present invention.

FIG. 6 a is an exploded perspective view of an MCT processing complex according to the present invention.

FIG. 6 b is an exploded perspective view of an MCT processing complex reaction portion according to a further embodiment of the present invention.

FIG. 6 c is an exploded perspective view of an MCT processing complex combustion portion according to a further embodiment of the present invention.

FIG. 7 a is a modified negative cutaway perspective view of the MCT processing complex shown in FIG. 6 a where channels are shown as solid regions.

FIG. 7 b is a rotated modified negative cutaway perspective view of the MCT processing complex shown in FIG. 7 a.

FIG. 8 a is a perspective view an MCT processing stack according to a further embodiment of the present invention.

FIG. 8 b is a rotated perspective view of the MCT processing stack shown in FIG. 8 a.

FIG. 9 is a perspective view of the MCT processing stack shown in FIG. 8 a illustrating stream headers and stream flows.

FIG. 10 is a plan view of the heat exchanger described in Example 1.

FIG. 11 a is a perspective view of a first end of the heat exchanger described in Example 1.

FIG. 11 b is a perspective view of a second end of the heat exchanger described in Example 1.

FIG. 12 shows the Volumetric Flowrates, Outlet Pressures, and Fluid Compositions for Example 1.

FIG. 13 shows the Inlet Temperatures for Example 1.

FIG. 14 shows the Outlet Temperatures for Example 1.

FIG. 15 shows the Pressure Drops for Example 1.

FIG. 16 shows a comparison of a heat exchanger according to the present invention with a computer simulation.

FIG. 17 shows the relationship of hydraulic diameter to heat transfer coefficient.

FIG. 18 shows an arrangement of channels exchanging heat wherein one fluid flows through a channel with heat enhancement fins.

FIG. 19 shows an arrangement of microchannels exchanging heat with no heat enhancement fins.

DETAILED DESCRIPTION OF THE INVENTION AND BEST MODE

The term “millichannel” refers to a channel having at least one internal dimension of width or height of up to about 10 mm.

The term “microchannel” refers to a channel having at least one internal dimension of width or height of up to about 2 mm, and in one embodiment from about 0.1 mm to about 2 mm, and in one embodiment from about 0.1 mm to about 1 mm. The length may be up to about 5 meters (m) or more. Preferably, the length is about 1 m or less. More preferably the length is about 0.5 m or less. A microchannel is also a millichannel.

A millichannel may be used in an apparatus in conjunction with microchannels for both heat exchanger applications and for combined heat exchange and reactor applications. The milli-channel offers the advantage of reduced pressure drop, but the disadvantage of lower heat transfer coefficients and surface area, including IPHTAP-type area. There are examples of when a process is advantaged by the inclusion of a milli-channel with microchannels for multiple fluid processing streams. As one example, if a relatively large fraction of heat greater than 70 percent were desired to be transferred from Fluid A to Fluid B and a much smaller fraction of heat from Fluid A to Fluid C in a single apparatus, then the Fluid C channels may be made in the milli-channel range. Combined exchanger and reactor applications may be advantaged by the inclusion of one or fluid milli-channel. As an example, in the limit of a very low pressure drop constraint on one or more fluids, such as combustion air, this channel may be designed in the milli-channel range. A very low pressure drop requirement for one fluid in a heat exchanger application may necessitate the use of a milli-channel. As one example, a process that utilized natural gas to provide home heating or power would be required to not exceed the allowable back pressure on the feed line, typically a few psi. Another advantage of a combined milli-channel and microchannel process is the combined application of homogeneous combustion with additional heat exchangers to preheat and recover heat. Heat recovery from combustion may take the form of heating water for portable or stationary applications. Homogeneous combustion is challenging in a microchannel for many hydrocarbon fuels, as the critical hydrocarbon quench diameter is often larger than a microchannel but well below the limits of a milli-channel. As an example, the quench diameter of methane exceeds 2 mm at room temperature and would not ignite in a microchannel. As the critical dimension increases from the microchannel range out to the broader milli-channel range, the overall size of the device may grow larger. For some applications, this is not disadvantageous if there are no space limitations. It will be appreciated by one skilled in the art, that many applications could be advantaged through the combinations of microchannels and milli-channels to tailor the performance of a process to meet desired specifications.

The term “microchannel” or “MCT” when applied to a device, process, system, or the like, means that such device, process, or system includes at least one microchannel.

The term “MCT processing unit” refers to a microchannel device having at least one reactor section and at least one heat exchanger section in combination.

The term “MCT processing system” refers to a plurality of MCT processing units in combination.

The term “MCT processing complex” refers to a plurality of MCT processing systems in combination.

The term “MCT processing stack” refers to a plurality of MCT processing complexes in combination.

The term “total core volume V” refers to the sum total volume of microchannels plus the volume of walls separating the microchannels, but specifically excluding any volume defined by any manifolds or headers. Thus, outside walls which define the outer dimensions of the device, are not included. Referring to FIGS. 1 a and 1 b, by way of example only, the total core volume V of the device shown would be computed as follows:

V=[(height 15a)*(width 15b)+(height 16a)*(width 16b)+(height 17a)*(width 17b)+(height 18)*(width 17b)+(height 15a)*(width 19)]*[length 14]

As will be understood by those skilled in the art, the total core volume V will be calculated based upon generally accepted principles of solid geometry and different configurations may be approached in different manners.

The term “total thermal power density” refers to the amount of heat gained by the cold stream(s) divided by the total core volume V.

The term “interstream planar heat transfer area percent” (IPHTAP) relates to the highest effective heat transfer and refers to the surface area that separates two fluids exchanging heat in a channel device excluding ribs, fins, and surface area enhancers as a percent of the total interior surface area of a channel that also includes ribs, fins, and surface area enhancers. That is, the ratio of the area through which heat is transferred to neighboring channels with a different fluid flowing to the total surface area of the channel. Referring to FIG. 18, an arrangement of channels is shown exchanging heat; there are three fluids, Fluid A, Fluid B, and Fluid C. Fluid A exchanges heat with Fluid B and with Fluid C. Channel A comprises heat enhancement fins (N/in.) as shown in FIG. 18. IPHTAP is calculated as [2a/(2a+2b+2c)]*100. In a typical compact heat exchanger, where a=2.0 in., b=0.5 in., and N=20 fins/in., IPHTAP equals 16 percent. A geometry with IPHTAP=100 percent would signify that all available area is utilized for exchanging heat with neighboring different streams. This example assumes that heat exchange at both long edges of the channel. If the channel is an end channel and exchanges heat at only one edge, IPHTAP=8 percent. In a microchannel, in contrast (FIG. 19), where a=2.0 in., b=0.025 in., d=0.040 in. and e=0.98 in., IPHTAP would be: Channel with Fluid A=[2a/(2a+2b)]*100=49 percent; Channel with Fluid B=[8c/(8c+8b)]*100=95 percent; Channel with Fluid C=[2e/(4e+4b)]*100=49 percent.

When used in this Specification, the terms “reactor”, “reaction”, “combustor”, “combustion”, “oxidizer”, and the like, when referring to microchannels and streams, are nominal only. It is to be understood that, within the scope and spirit of the present invention, no reaction or any reaction and no combustion or any similar combustion or exothermic reaction may take place within such named microchannels. By way of example only, reactions may include catalytic processes such as acetylation, addition reactions, alkylation, dealkylation, hydrodealkylation, reductive alkylation, amination, aromatization, arylation, autothermal reforming, carbonylation, decarbonylation, reductive carbonylation, carboxylation, reductive carboxylation, reductive coupling, condensation, cracking, hydrocracking, cyclization, cyclooligomerization, dehalogenation, dimerization, epoxidation, esterification, exchange, Fischer-Tropsch, halogenation, hydrohalogenation, homologation, hydration, dehydration, hydrogenation, dehydrogenation, hydro carboxylation, hydroformylation, hydrogenolysis, hydrometallation, hydrosilation, hydrolysis, hydrotreating, hydrodesulferization/hydrodenitrogenation (HDS/HDN), isomerization, methanation, methanol synthesis, methylation, demethylation, metathesis, nitration, oxidation, partial oxidation, polymerization, reduction, Sabatier reaction, steam and carbon dioxide reforming, sulfonation, telomerization, transesterification, trimerization, water gas shift (WGS), and reverse water gas shift (RWGS). By further example, phase changes such as condensation and evaporation are also within the contemplation of the present invention, as are operations such as absorption and adsorption.

Referring initially to FIGS. 1 a-1 d, the MCT heat exchanger 10 of the present invention has a total core volume V and comprises a first microchannel 12 a, a second microchannel 12 b, and at least a third microchannel 12 c. In operation, a first stream 20, a second stream 22, and at least a third stream 24 flow through the first microchannel 12 a, the second microchannel 12 b, and the at least third microchannel 12 c, respectively. While FIG. 1 d illustrates a single-pass, parallel counter/co-current flow pattern, it will be understood by those skilled in the art that the flow pattern may be any of suitable design. Multiple pass flows as well as co-current and cross-current flow patterns (shown in FIGS. 2 a-2 c) are possible. Importantly, the total thermal power densities of such devices can be from about one (1) W/cc to 40 W/cc or more, the total pressure drop can be 0.25 psi per in. or less, and the interstream planar heat transfer area percent greater than 10 percent. Particular attention is drawn to the shapes, sizes, and separations of the first microchannel 12 a, the second microchannel 12 b, and the at least third microchannel 12 c. By varying the dimensions and overall design format of the microchannel layout and the walls separating the microchannels, the flow of heat energy between streams can be varied virtually infinitely. It is also possible to provide a higher heat transfer rate per unit volume, less metal between microchannels is required, and a higher heat transfer coefficient per hydraulic diameter. Thus,

-   -   ˜f(D_(h)), where         is the heat transfer coefficient, D_(h) is the hydraulic         diameter, and     -   D_(h)=4A/P, where A is the cross-sectional area and P is the         wetted perimeter.         As is shown, for example, in FIG. 16, heat transfer         coefficients,         increase as the hydraulic diameter, D_(h), decreases.

Consider, first, the overall size of the device; the width, length, and height. A larger overall size leads to higher total heat capacities and less relative heat loss (Q_(loss)/Q_(total)) but also leads to difficulties in manifolding and flow distribution. In a counter-current flow heat exchanger, a larger heat exchanger length gives a smaller average approach temperature between the hot and cold streams. That is, T_(hot-exit-mean)−T_(cold-inlet-mean). However, a smaller approach temperature also indicates lower transversal heat flux between the streams. Consider, next, the thermal properties of the device; including the thermal conductivity, specific heat, and density. A higher thermal conductivity gives a higher transversal heat transfer rate but also higher longitudinal heat conduction. The former will enhance the heat transfer between the streams in adjacent channels. The latter is undesirable because it degrades the heat exchange performance due to larger approach temperatures. An optimal thermal conductivity for a given structure and dimensions for microchannel heat exchangers can be determined. See, e.g., T. Stief et al., Numerical Investigations on Optimal Heat Conductivity in Micro Heat Exchangers, AIChE 2000 Spring Meeting (Mar. 2-9, 2000). Larger specific heats and densities lead to higher thermal inertia and, therefore, a slow transition of operation statuses, for example start-up and shut-down. Consider, next, the total flow rate, or capacity, of an individual stream. The increase in flow rate generally leads to a smaller temperature drop of a hot stream (or to a smaller increase in temperature of a cold stream) throughout the exchanger. This also means that the overall approach temperature of all the streams will increase. If the flow rates of other streams remain unchanged, the local heat flux will increase by increasing the flow rate of one stream. A decrease in the microchannel dimension leads to an increase in the heat transfer coefficient and, in turn, the heat flux between the fluid in the microchannel and the microchannel wall. For a cold stream, its exit temperature becomes higher, for the same mass flux, than it was before reducing the size of the microchannel dimension. The overall thermal effectiveness is increased because the amount of heat transferred from or to the other streams also increases. However, the increase in the amount of heat transferred from or to the other streams is generally smaller than that of the stream whose microchannel dimension is reduced. There is, however, a practical lower limit since the lower the microchannel dimension, the higher the pressure drop. In the present invention, a microchannel having a rectangular cross-section is preferred as this geometry gives higher heat transfer coefficients and less solid material is required than with a square or round channel. Particularly, very wide microchannels with a very small microchannels can nearly isolate a particular stream from thermal communication with other streams. A spacer or rib in, or between streams, may function as a fin to improve the heat transfer between the stream and the solid wall and, in turn, improve the heat transfer to other streams. This effect is also found in ribs, webs, and spacers between different streams at temperatures lower than local wall temperatures. However, one of the effects of increasing the dimensions of webs, ribs, spacers, and perimeter metal is to increase the unwanted metal cross-sectional area and, in turn, the axial conduction. Another effect of increasing dimensions of webs between different streams is to increase the resistance of transverse heat conduction when heat transfer between the two streams is desired. These two effects decrease the transverse heat flux between different streams and, therefore, degrade the heat exchange performance.

As will be appreciated by those skilled in the art, the choice of microchannel cross-section is not limited to rectangular; other polygonal and even circular or elliptical cross-sections can be used within the scope of the present invention.

Referring now to FIGS. 2 a-2 c, in another embodiment of the present invention, an MCT heat exchanger has at least four surfaces 34, 36 (indicated but not shown), 38, and 40 (indicated but not shown), and comprises a first microchannel 32 a, a second microchannel 32 b, and at least a third microchannel 32 c. In operation, a first stream 42, a second stream 44, and at least a third stream 46 flow through the first microchannel 32 a, the second microchannel 32 b, and the at least third microchannel 32 c, respectively. Illustratively, the third microchannel 32 c may further comprise a plurality of interior walls or ribs 33. As will be appreciated by those skilled in the art, the ribs 33 introduce significant design flexibility and allow a virtually limitless combination of hydraulic diameters. In addition, the ribs 33 can, in appropriate circumstances, help provide additional structural support when dealing with pressure differentials across the walls separating one microchannel from another. While FIGS. 2 a-2 c illustrate a single-pass flow pattern, it will be understood by those skilled in the art that the flow pattern may be of any suitable design. In addition, one skilled in the art will appreciate that the angles between the faces need not be exact right angles as shown; many other angles will be effective depending upon the application. Importantly, however, the total thermal power density of such devices can be about 21 W/cc to 40 W/cc or more.

As will be further appreciated by those skilled in the art, the usefulness of the present invention is not limited to the specific configurations illustrated in FIGS. 1 a-1d and 2 a-2 c. By way of example only, the various microchannels may vary in number, size, and complexity. The relative positions of one microchannel to other microchannels may also be varied as may the thickness as well as the inherent thermal conductivity of the walls separating one microchannel from the other microchannels. See discussion herein above.

Example 1

Referring now to FIGS. 10-15, a heat exchanger was specifically designed to simulate a heat exchanger according to one embodiment of the present invention. The heat exchanger used five distinct fluids, denoted in FIGS. 10-15 as Fluids A, B, C, D, and E. Fluids C and D were split into two streams each with each stream flowing through separate microchannels; fluids A, B, and E each flowed through separate microchannels (as Streams A, B, and E, respectively), making a total of seven microchannels in the heat exchanger. As shown in FIG. 10, Fluid C flowed through two microchannels as Stream C1 and Stream C2. Similarly, Fluid D flowed through two microchannels as Stream D1 and D2. The experimental results show the performance of the heat exchanger and the results as compared to numerical simulations from a computer program.

Referring again to FIG. 10, the heat exchanger consisted of seven rectangular microchannels, each ten inches (in.) long. The height of each microchannel where Streams A and B flowed was 0.020 in. The height of the microchannel where Stream E flowed was 0.040 in. The height of each microchannel where Stream D1 and Stream D2 flowed was 0.020 in., and the heights of the microchannels where Streams C1 and C2 flowed were 0.030 in. and 0.020 in., respectively. The order of the seven streams in the heat exchanger was C1, D1, A, B, E, C2, and D2 (shown in FIG. 10). (For clarity and consistency, the heat exchanger microchannels are referred to by the name of the stream flowing through them. Thus, Stream C1 flows through microchannel C1.)

The heat exchanger was constructed of Inconnel 625 and the microchannels were made by “popping” a 0.030-in. diameter hole with an electrode in the places where the rectangular microchannels were needed. After the holes were made, microchannels were made by using wire ElectroDischarge Machining (EDM). If the microchannel width was less than 0.030 in., the edge portions of the original round hole still existed around the outside of the microchannel; the portions of the original hole were purposely, alternatingly, offset to the top and bottom of the microchannels. If the microchannel width was equal to or greater than 0.030 in., no portions of the round hole remained.

Referring to FIGS. 11 a and 11 b, manifolding for the inlet of Microchannel C2 was accomplished by sending Stream C2 directly into the device while manifolding for the outlet of Microchannel C1 was accomplished by exiting Stream C1 directly out from the device; the other microchannels were blocked off by welding the microchannels closed on the front and back faces. The inlet to Microchannel C1 was manifolded by drilling in through the side of the heat exchanger. The outlet from Microchannel C1 came directly out of the heat exchanger similar to Microchannel C2. Microchannel D2 on the edge of the heat exchanger was also manifolded in and out of the side of the heat exchanger. The other microchannels in the center of the heat exchanger were manifolded in the top and bottom of the heat exchanger. The diameter of the inlet and outlet holes was equal to or smaller than the width of the channel, i.e., 0.020 in. to 0.040 in. Generally, three or four holes that served as the inlet or exit were drilled into each such microchannel.

The exact composition and flowrates of each of the streams for each test are shown in FIG. 12. Experiments were performed with flowrates corresponding to six conditions. The first two conditions were nearly equivalent except that the reactant and product streams entered the heat exchanger at approximately one-half the expected pressure.

Experiments were performed at the temperatures and pressures shown in FIGS. 12 and 13. The directions of the streams are shown in FIGS. 11 a and 11 b. Streams A, C1, C2 flow in the same direction and counter-current to the flow of Streams B, D1, D2, and E.

There were three sets of experimental tests performed for the heat exchanger; Tests X, Y, and Z as shown in FIGS. 12-15. The pressure drops of some of the streams are shown in FIG. 15; all pressure drops were measured before and after the fluid entered and exited the microchannel, therefore contraction and expansion losses are included in the measured pressure losses. The pressure losses of the individual streams were measured with differential pressure gauges, most of which measured a maximum differential pressure of 5.4 psi and a resolution of 0.1 psi. The stream labeled D1 was measured with a meter capable of measuring 9.0 psi and a resolution of 0.2 psi.

The five-stream heat exchanger demonstrated that a multi-stream microchannel heat exchanger could successfully heat and cool multiple streams in a single device. There was reasonable agreement with a numerical simulation that was constructed. The comparison between the experimental values and the results from the numerical simulation are shown in FIG. 16. The inlet temperatures were fixed and the outlet temperatures calculated.

An approach temperature was also calculated:

${T_{m} = \frac{\sum\limits_{i = 1}^{n}{T_{i} \cdot m_{i} \cdot {Cp}_{i}}}{\sum\limits_{i = 1}^{n}{m_{i} \cdot {Cp}_{i}}}},$

where T_(m) is the mean temperature of the hot streams at a first end of the heat exchanger and is also used to calculate the mean temperature of the cold streams at the first end, the mean temperature of the hot streams at the second end, and the mean temperature of the cold streams at the second end. T_(i) is the ith hot stream, m_(i) is the mass flow rate (kg/s) of the ith hot stream, Cp_(i) is the heat capacity of the ith hot stream. The mean temperature of the hot streams at the first end was 857 deg. C. and at the second end 250 deg. C. The mean temperature of cold streams at the first end 730 deg. C. and at the second end 161 deg. C. The mean approach temperatures are: 126 deg. C. at the first end and 89 deg. C. at the second end.

Referring now to FIG. 3 a, in another embodiment of the present invention, an MCT processing unit 50 has a total core volume V (not shown) and comprises a reactor microchannel 52, a combustor microchannel 62, and an oxidizer microchannel 72. The reactor microchannel 52 comprises a first reactor heat exchange microchannel 54, a reaction microchannel 56, and a second reactor heat exchange microchannel 58. Alternatively, only one reactor heat exchange microchannel may be present. Also, as will be understood by those skilled in the art, the precise point where the reactor microchannel 52 is no longer primarily exchanging heat and is functioning primarily as a reactor can be difficult to determine and can be somewhat arbitrary. For example, the reactor microchannel 52 may be in thermal communication with one or more other microchannels in the same unit. The reaction microchannel 56 may further include a reaction catalyst 60. The reaction catalyst 60 may contain any suitable metal or semi-metal and/or their oxides comprising one or more elements from Groups IIIA, IVA, VA, VIIA, VIIIA, IB, IIB, IIIB, IVB, Ce, Pr, Sm, Tb, Th or their oxides and combinations thereof. The reaction catalyst 60 may also contain promoters which enhance the chemical or physical properties of the reaction catalyst 60, and may contain any suitable metal, semi-metal or non-metal, and/or their oxides, comprising one or more elements from the previous list and/or Group IA, IIA, VB, VIB and combinations thereof. The reaction catalyst 60 may also be supported on any suitable support material, such as silica, alumina, zirconia, titania, magnesia, yttria, ceria, lanthana, carbon or combinations of these, which supply either sufficient surface area or chemical interaction to benefit the action of the active constituent. The reaction catalyst 60, by way of example only, may be applied to an engineered substrate such as a felt, foam, fin, mesh, gauze, or foil and the substrate inserted into a cutout (not shown) in a wall of the reaction microchannel 56 to act as a flow-by catalyst, may be inserted into the reaction microchannel 56 to act as a flow-through catalyst, or may be applied to a wall or walls of the reaction microchannel 56 as a washcoat. Thus, the reaction catalyst 60 may be present in the form of a powder or small pellet, a monolith, a wall coating or combinations of these forms. In the case of powders and monoliths, the reaction catalyst 60 may be comprised of a skeletal, or Raney type, metal. In the case of a monolith, the reaction catalyst 60 may be present as a slurry or wash coating on a foam, felt, screen, mesh, gauze or similar substrate. In the case of a wall coating, the reaction catalyst 60 may be applied as by slurry coating or direct wash coating, preferably with prior treatment of the wall in such a way as to maximize adhesion and/or surface area. In some cases, constituents of the reaction catalyst 60 may be comprised wholly or partially from native materials present in the wall or monolith alloys. The reaction catalyst 60 may also include two or more different catalyst types in different regions of the reaction microchannel 56. Alternatively, depending upon the desired reaction, the reaction microchannel 56 may include no reaction catalyst 60. Finally, there may be no reaction in reaction microchannel 56, for example, when vaporizing a liquid stream.

The combustor microchannel 62 comprises a first combustor heat exchange microchannel 64, a combustion microchannel 66, and a second combustor heat exchange microchannel 68. As with the reactor microchannel 52, alternatively, only one combustor heat exchange microchannel may be present. Also, as with the reactor microchannel 52, as will be understood by those skilled in the art, the precise point where the combustor microchannel 62 is no longer primarily exchanging heat and is functioning primarily as a combustor can be difficult to determine and somewhat arbitrary. And, in fact, combustion and significant heat exchange can, and does, occur in the same region of the combustor microchannel 62. For example, the combustor microchannel 62 may be in thermal communication with one or more other microchannels in the same device. The combustion microchannel 66 may also include a combustion catalyst 70. To provide further flexibility, the first combustor heat exchange microchannel 64 and the second heat exchange microchannel 68 may also include a combustion catalyst 70 to provide pre- and post-oxidation reactions. The combustion catalyst may contain any suitable active metal and/or metal oxide, preferably comprising one or more elements from Groups IIIA, VIIIA or IB, Ce, Pr, Sm or their oxides and combination thereof, or more preferably comprising one or more of the elements Pt, Pd, Y, La, Ce, Pr or their oxides, and combinations thereof. The combustion catalyst 70 may also be supported on any suitable support material, such as silica, alumina, zirconia, titania, magnesia, yttria, ceria, lanthana, carbon or combinations thereof, which supply either sufficient surface area or chemical interaction to benefit the action of the active constituent. The combustion catalyst 70 may be present in the form of a powder or small pellet, a monolith, a wall coating or combinations of these forms. In the case of powders and monoliths, the combustion catalyst 70 may be comprised of a skeletal, or Raney type, metal. In the case of a monolith, the combustion catalyst 70 may be present as a slurry or wash coating on a foam, felt, screen, mesh, gauze or similar substrate. In the case of a wall coating, the combustion catalyst 70 may be applied as by slurry coating or direct wash coating, preferably with prior treatment of the wall in such a way as to maximize adhesion and/or surface area. In some cases, constituents of the combustion catalyst 70 may be comprised wholly or partially of native materials present in the wall or monolith alloys. Alternatively, depending upon the desired combustion, the combustion microchannel 66, the first combustor heat exchange microchannel 64, and the second combustor heat exchange microchannel 68 may include no combustion catalyst 70. As will be appreciated by those skilled in the art, combustion may be replaced with any number of exothermic reactions. By way of example only, acetylation, alkylation, hydrodealkylation, epoxidation, Fischer-Tropsch, hydration, dehydration, hydrogenation, oxidative dehydrogenation, hydrolysis, methanation, methanol synthesis, metathesis, oxidation, polymerization, and water-gas shift (WGS).

The oxidizer microchannel 72 comprises one or more apertures 74 through which the oxidizer microchannel 72 is in fluid communication with the combustor microchannel 62. As with the combustor microchannel 62, the oxidizer microchannel 72 may provide for the introduction of other reactants to an exothermic reaction.

In operation, by way of example only, a reactants stream 75, such as a mixture of steam and methane, is introduced into the reactor microchannel 52 at the first reactor heat exchange microchannel 54. A fuel stream 77, such as hydrogen or methane or other hydrocarbon, is introduced into the combustor microchannel 62 at the first combustor heat exchange microchannel 64, and an oxidizer stream 78, such as air, is introduced into the oxidizer microchannel 72. As the reactants stream 75 flows through the reaction microchannel 56 it is converted, for example, in a reforming reaction, to the products stream 58, such as a mixture of steam, methane, and hydrogen. A reaction catalyst 60 is used. As the fuel stream 77 flows through the first combustor heat exchange microchannel 64 and the combustion microchannel 66, it becomes combined with oxidizer 78 introduced into the oxidizer microchannel 72 and thus into the combustor microchannel 64 via the one or more apertures 74, and combusts to form the exhaust stream 79. A combustion catalyst 70 may be used. Note that pre-oxidation may occur in the first combustor heat exchange microchannel 64 to preheat the reactants stream 75. Likewise, oxidation may continue into the second combustor heat exchange microchannel 68 to provide additional heat energy downstream of the combustion microchannel 66. By further example only, the reaction converting the reactants stream 75 into the products stream 76 is an endothermic reaction such as steam methane reforming or hydrocarbon dehydrogenation, the fuel stream 77 is hydrogen or a combination of carbonaceous fuels, and the oxidizer stream 78 is air.

As will be appreciated by those skilled in the art, the present invention, embodiments of which are represented and described herein, may be useful for unit operations where there is only a single reaction. By way of example only, reactor microchannel 52 may serve as a vaporizer. Similarly, an MCT device may comprise a first combustor microchannel in thermal communication with a second combustor microchannel, the combustor microchannels supported by one or more oxidizer microchannels. And, as discussed herein above, oxidative combustion need not be one of the reactions involved. To further illustrate the flexibility of the present invention, FIG. 3 b shows a modification of the MCT processing unit 50 of FIG. 3 a. All descriptions in FIG. 3 a are attributable to FIG. 3 b but the flow is shown in a countercurrent pattern.

FIG. 4 shows another embodiment of the present invention. An MCT processing unit 80 has a total core volume V (not shown) and comprises a reactor microchannel 82, a combustor microchannel 92, and an oxidizer microchannel 102. The reactor microchannel 82 comprises a first reactor heat exchange microchannel 84, a reaction microchannel 86, and a second reactor heat exchange microchannel 88. Alternatively, only one reactor heat exchange microchannel may be present. Also, as will be understood by those skilled in the art, the precise point where the reactor microchannel 82 is functioning primarily as a reactor or not can be difficult to determine and can be somewhat arbitrary. For example, the reactor microchannel 82 may be in thermal communication with one or more other microchannels in the same device. The reaction microchannel 86 may further include a reaction catalyst 90. Alternatively, depending upon the desired reaction, the reaction microchannel 86 may include no reaction catalyst 90.

The combustor microchannel 92 comprises a first combustor heat exchange microchannel 94, a combustion microchannel 96, and a second combustor heat exchange microchannel 98. As with the reactor microchannel 82, alternatively, only one combustor heat exchange microchannel may be present. Also, as with the reactor microchannel 82, as will be understood by those skilled in the art, the precise point where the combustor microchannel 92 is no longer primarily exchanging heat and is functioning primarily as a combustor can be difficult to determine and somewhat arbitrary. For example, the combustor microchannel 92 may be in thermal communication with one or more other microchannels in the same device. The combustion microchannel 96 may also include a combustion catalyst 100. To provide further flexibility, the first combustor heat exchange microchannel 94 and the second heat exchange microchannel 98 may also include combustion catalyst 100. The combustion catalyst 100 may be [different types of catalysts and different methods of applying]. Alternatively, depending upon the desired combustion, the combustion microchannel 96, the first combustor heat exchange microchannel 94, and the second combustor heat exchange microchannel 98 may include no combustion catalyst 100.

The oxidizer microchannel 102 comprises one or more apertures 104 through which the oxidizer microchannel 102 is in fluid communication with the combustor microchannel 92.

Operation of the MCT processing unit 80, by way of example only, is analogous to that described herein above in reference to the MCT processing unit 50.

As will be appreciated by those skilled in the art, the apertures 74 (shown in FIGS. 3 a and 3 b) and the apertures 104 (shown in FIG. 4) add yet another dimension to the design flexibility of the present invention. By varying the placement, cross-section, shape, and size of a plurality of apertures 74 and of a plurality of apertures 104, significant flexibility can be achieved in combining two or more streams. Likewise, the thickness of the material through which the apertures 74 and the apertures 104 are created can add yet another dimension to the design flexibility. By changing these variables, the mixing or fluid communication between the two streams can be uniquely controlled. By way of example only, in a combustion application, the temperature profile and the heat transferred can be tailored to the particular application and reactor design. This is achieved because the oxidizer stream 78 acts as a limiting agent in a combustion reaction. Thus, the apertures 74 and apertures 104 function to introduce specific amounts of the oxidizer stream 78 to specific points so as to control the rate and extent of the combustion reaction along the entire length of the combustor microchannel 62 and combustor microchannel 92.

Referring now to FIG. 5, an MCT processing system 110 has a total core volume V (not shown) and comprises a plurality of MCT processing units 111, a first termination microchannel 136, and a second termination microchannel 138. As will be understood by those skilled in the art, the choice of termination modes may be varied according to the design requirements of the MCT processing system 110. As discussed herein above, to realize the advantages of MCT, multiple MCT processing units 111 must be combined into an integrated system to approach the total throughput of a large-scale operation. The MCT processing system 110 helps accomplish that by integrating a plurality of MCT processing units 111, the basic technology of which has been introduced herein above.

Each MCT processing unit 111 comprises a first reactor microchannel 112, a second reactor microchannel 113, a first combustor microchannel 122, a second combustor microchannel 123, a first oxidizer microchannel 132, and a second oxidizer microchannel 133. The first reactor microchannel 112 comprises a first reactor heat exchange microchannel 114, a first reaction microchannel 116, and a third reactor heat exchange microchannel 118. The second reactor microchannel 113 comprises a second reactor heat exchange microchannel 115 and a second reaction microchannel 117 and is in fluid communication with the third reactor heat exchange microchannel 118. The first reaction microchannel 116 may also include a reaction catalyst 120. The second reaction microchannel 117 may also include a reaction catalyst 120. Preferably, as shown in FIG. 5, a reactor microchannel tongue 140 is also included.

The first combustor microchannel 122 comprises a first combustor heat exchange microchannel 124, a first combustion microchannel 126, and a third combustor heat exchange microchannel 128. The second combustor microchannel 123 comprises a second combustor heat exchange microchannel 125 and a second combustion microchannel 127 and is in fluid communication with the third combustor heat exchange microchannel 128. The first combustion microchannel 126 may also include a combustion catalyst 130. The second combustion microchannel 127 may also include a combustion catalyst 130. Preferably, as shown in FIG. 5, a combustor microchannel tongue 142 is also included. The reactor microchannel tongue 140 and the combustor microchannel tongue 142 provide flow stabilization and, if non-rigid, flow equalization to overcome minor variations in microchannel dimensions.

The first oxidizer microchannel 132 comprises at least one aperture 134 through which the first oxidizer microchannel 132 is in fluid communication with the first combustor microchannel 126. The second oxidizer microchannel 133 comprises at least one aperture 134 through which the second oxidizer microchannel 133 is in fluid communication with the second combustor microchannel 123.

Operation of each MCT processing unit 111, by way of example only, is analogous to that described herein above in reference to the MCT processing unit 50 and the MCT processing unit 80.

Referring now to FIG. 6 a, an MCT processing complex 210 has a total core volume V (not shown) and comprises a plurality of MCT processing systems 110 (best illustrated in FIG. 5), a first reactants manifold 212, a second reactants manifold 214, a products manifold 216, a first fuel manifold 218, and a second fuel manifold 220. As will be appreciated by those skilled in the art, the precise arrangement of each manifold is subject to various design considerations and it is within the scope and intent of the present invention to include other such arrangements. By way of example only, the first fuel manifold 218, the second fuel manifold 220, the first reactants manifold 212, and the second reactants manifold 214 the first reactants manifold 212, and the second reactants manifold 214 all terminate on the same face of the MCT processing complex 210 but at different positions along an external face of the MCT processing complex 210. (Also seen in FIGS. 8 a and 8 b.) As will further be appreciated by those skilled in the art, an exhaust manifold (not shown) could also be included to collect fluids exiting the third combustor heat exchange microchannels 128. By way of further illustration, FIGS. 7 a and 7 b show a partial cutaway negative wireframe view of the microchannel arrangement shown in FIG. 6 a. In addition to a plurality of MCT processing systems 110, it is preferable to repeat the MCT processing complex 210 to form an MCT processing stack 310 (illustrated in FIGS. 8 and 9) capable of high throughput.

FIGS. 6 b and 6 c illustrate a further embodiment of the present invention for manifolding the various microchannels. For example, a reactants flue 213 a provides fluid communication between a plurality of first reactor microchannels 116 and an outside surface of the MCT processing complex 210 via the first reactants manifold 212 and a first reactants manifold stub 213 and between a plurality of second reactants microchannels 117 and an outside surface of the MCT processing complex 210 via the second reactants manifold 214 and a second reactants manifold stub 215. Likewise, a products flue 217 a provides analogous fluid communication for a plurality of third reactor heat exchange microchannels 118, a fuel flue 219 a provides analogous fluid communication for a plurality of first combustor microchannels 122 and a plurality of second combustor microchannels 123, and the oxidizer flue 223 a provides analogous fluid communication for a plurality of first oxidizer microchannels 132 and a plurality of second oxidizer microchannels 133. As will be appreciated by those skilled in the art, an exhaust flue may provide fluid communication between a plurality of third combustor heat exchange microchannels 128, thus further illustrating the design flexibility of the present invention. In addition, by way of example only, the orientations of the first reactants manifold stub 213, the first reactants manifold 212, and the plurality of first reactor microchannels 116 relative to one another is virtually infinitely flexible. Thus, allowing even further design flexibility depending upon the specific application.

Referring now to FIGS. 8 a and 8 b, an MCT processing stack 310 has a total core volume V (not shown) and comprises a plurality of MCT processing complexes 210. Shown in FIG. 8 a are a plurality of first fuel manifolds 218 and second fuel manifolds 220 in substantial linear alignment, a plurality of first reactants manifolds 212 and second reactants manifolds 214 in substantial linear alignment, and a plurality of third combustion heat exchanger microchannels 128 in substantial linear alignment. Shown in FIG. 8 b are a plurality of first oxidizer manifolds 222 and second oxidizer manifolds 224 in substantial linear alignment, and a plurality of products manifolds 216 in substantial linear alignment. While FIGS. 8 a and 8 b illustrate a specific relational arrangement of manifolds and the plurality of third combustor heat exchange microchannels 128, it will be understood by one skilled in the art that other arrangements are possible.

Referring now to FIG. 9, an MCT processing stack 310 comprises a plurality of MCT processing complexes 210, a reactants header 312, a products header 314, a fuel header 316, an oxidizer header 318, and an exhaust header 320. As will be appreciated by those skilled in the art, the precise arrangement of each manifold is subject to various design considerations and it is within the scope and intent of the present invention to include other such arrangements.

Fabrication of the MCT processing stack 310 is by know techniques. The MCT processing complexes 210 are made as first subassemblies. The headers 312, 314, 316, 318 are then conventionally welded onto the exterior of the subassemblies. The heating rate during welding must be closely monitored to ensure a high level of quality; hot spots may damage the subassemblies, including delamination. In addition to welding on the headers 312, 314, 316, 318, the subassemblies themselves may be welded into place on any form of infrastructure. This infrastructure, by way of example only, may serve as outer protection, fixing the device in space, safety containment, insulation, cooling jacket, and lifting points.

In operation, by way of example only, a reactants stream 75 is introduced into the reactants header 312, a products stream 76 is discharged from the products header 314, a fuel stream 77 is introduced into the fuel header 316, an oxidizer stream 78 is introduced into the oxidizer header 318, and the exhaust stream 79 is discharged form the exhaust header 320. The embodiment shown in FIGS. 8 a-9 shows a plurality of integral heat exchanger and reactor combinations. There are five distinct fluid streams: The reactants stream 75, the products stream 76, the oxidizer stream 78, the fuel stream 77, and the exhaust stream 79. As shown in the accompanying figures, the exhaust stream 79 exits straight out of each MCT processing complex 210 via each third combustor heat exchange microchannel 128. Alternatively, any of the other streams could be headered straight off each MCT processing complex 210. The exhaust stream 79 was selected to minimize the overall pressure drop of the oxidizer stream 78-fuel stream 77-exhaust stream 79 system. The four remaining streams are headered on the sides of each MCT processing complex 210 and, thus, on the sides of the MCT processing stack 310. Each fluid stream enters or exits at different points along the length of each MCT processing complex 210. For multi-stream devices, therefore, fluids may enter or exit at different points of the MCT processing complex 210, thus allowing much design flexibility in the thermal profile. For example, streams that enter much warmer than other streams may be selected to be headered further down the length, or toward warmer sections of the device. Thus, advantage is taken of the monotonically increasing temperature profile feature of the device. The heights of the manifolds is selected to generally minimize overall pressure drop while still allowing for good flow distribution among the internal array of microchannels. Smaller heights may be utilized where higher pressure drops can be tolerated.

CLOSURE

While embodiments of the present invention have been shown and described, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the Specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims. 

1. An apparatus, comprising: a first microchannel, having an inlet thereto and an outlet therefrom; a second microchannel, having an inlet thereto and an outlet therefrom; and at least a third microchannel, having an inlet thereto and an outlet therefrom, wherein each inlet and each outlet is distinct from the other inlets or outlets, respectively.
 2. The apparatus of claim 1, further comprising: a plurality of first microchannels, each first microchannel having an inlet thereto and an outlet therefrom; a plurality of second microchannels, each second microchannel having an inlet thereto and an outlet therefrom; and a plurality of at least third microchannels, each at least third microchannel having an inlet thereto and an outlet therefrom, wherein each inlet and each outlet is distinct from the other inlets or outlets, respectively.
 3. The apparatus of claim 1, further including a fluid flowing in the first microchannel, the fluid having a Reynolds number of less than about 4,000.
 4. The apparatus of claim 1, wherein the IPHTAP of at least one microchannel is about 30 or greater.
 5. The apparatus of claim 1, wherein at least one microchannel has at least one internal dimension of width or height of about 0.1 mm or less.
 6. The apparatus of claim 1, wherein when a first fluid flows through the first microchannel, the IPHTAP is about 30 or greater.
 7. The apparatus of claim 6, wherein when a first fluid is flowing through the first microchannel, a second fluid is flowing through the second microchannel, and an at least third fluid is flowing through the at least third microchannel, the total thermal power density is greater than 1 W/cc.
 8. The apparatus of claim 1, wherein the first microchannel has a hydraulic diameter different from at least the second microchannel.
 9. The apparatus of claim 8, wherein when a first fluid flows through the first microchannel, a second fluid flows through the second microchannel, and an at least third fluid flows through the at least third microchannel, the IPHTAP of at least one microchannel is about 10 or greater.
 10. The apparatus of claim 1, further comprising: a first surface; a second surface, in a substantially opposing and spaced-apart relation to the first surface; a third surface, in a substantially orthogonal relation to the first surface and to the second surface; and a fourth surface, in a substantially opposing and spaced-apart relation to the third surface, wherein: the first microchannel defines a passageway between the first surface and the second surface; the second microchannel defines a passageway between the first surface and the second surface; and the at least third microchannel defines a passageway between the third surface and the fourth surface, wherein the first microchannel has a cross-sectional area different from at least the second microchannel or the third microchannel.
 11. The apparatus of claim 10, wherein at least one microchannel has at least one internal dimension of width or height of about 2 mm or less.
 12. The apparatus of claim 11, wherein at least one microchannel has at least one internal dimension of width or height of about 0.1 mm or less.
 13. A process, comprising: (a) flowing a first stream, having a first temperature, through the first microchannel of the apparatus of claim 1; (b) flowing a second stream, having a second temperature, through the second microchannel of the apparatus of claim 1; and (c) flowing a third stream, having a third temperature, through the at least third microchannel of the apparatus of claim
 1. 14. The process of claim 13, wherein the first stream is flowing at a Reynolds number of about 4,000 or less.
 15. The process of claim 13, wherein the residence time of the first stream is about 500 ms or less.
 16. The process of claim 13, wherein the first stream is a gaseous fluid and flows through the first microchannel at a pressure drop of about 15 psi or less.
 17. The process of claim 13, further comprising: (a) placing the first stream in thermal communication with the second stream and the at least third stream.
 18. The process of claim 17, wherein when the first stream is a gaseous fluid, and flows through the first microchannel at a pressure drop of about 15 psi or less.
 19. The process of claim 18, wherein the residence time of the first gaseous fluid stream is about 500 ms or less.
 20. The process of claim 17, wherein the IPHTAP of at least one microchannel is about 30 or greater.
 21. A process, comprising: (a) flowing a first fluid through a plurality of first microchannels; (b) flowing a second fluid through a plurality of second microchannels; and (c) flowing at least a third fluid through a plurality of at least third microchannels, the plurality of at least third microchannels being in thermal communication with the plurality of first microchannels and with the plurality of second microchannels.
 22. The process of claim 21, wherein the total thermal power density is greater than about 1 W/cc.
 23. An apparatus, comprising: a first end and a second end; a first microchannel; a second microchannel; a third microchannel; a fourth microchannel; a fifth microchannel; a sixth microchannel; and a seventh microchannel, each microchannel defining a passageway between the first end and the second end, wherein each microchannel is in thermal communication with at least one of the other microchannels and the first microchannel has a cross-sectional area different from at least the second microchannel.
 24. The apparatus of claim 23, wherein when a first portion of a first gaseous fluid, at a first temperature flows through the first microchannel, a first portion of a second gaseous fluid, at a second temperature flows through the second microchannel, a third gaseous fluid, at a third temperature flows through the third microchannel, a fourth gaseous fluid, at a fourth temperature flows through the fourth microchannel, a fifth gaseous fluid, at a fifth temperature flows through the fifth microchannel, a second portion of the first gaseous fluid, flows through the sixth microchannel, and a second portion of the second gaseous fluid, flows through the seventh microchannel, the total thermal power density of the heat exchanger is at least 1 W/cc.
 25. The apparatus of claim 23, wherein the weighted average approach is about 150 deg. C. 